There are many environments in which it is desirable to have a quarter turn or quick release coupling device that can withstand high shear stresses when coupling two thin members together particularly when the thin members are provided with oversized holes for facilitating assembly and passage of the fastener therethrough. A specific example of this type of environment is in the coupling together of sections of highway guard rails that are subject to damage caused by high impact from motor vehicles tending to pull the two coupled sections apart. The guard rails are designed so that they can be assembled quickly and disassembled quickly so that a damaged section can be readily replaced.
The difficulty that arises with conventional type of fasteners employed today is that when the guard rail is struck by a vehicle, the two adjacent sections will tend to pull apart thereby rotating the fastener mounted in the corresponding slots in the two sections so as to reposition the fastener in a location that it is subjected to a tension load rather then the natural shear load to which it would have been subjected in the original position and which it is constructed to withstand. Oversized holes are conventional because they add to the ease of assembly and disassembly of the adjacent elements. Therefore, the advantage gained in assembly time is lost in rigidity since rotation of the fastener is possible. Furthermore, even if the holes were designed to be slightly larger than the fastener element therethrough, the fact that the material used for the guard rails are relatively thin in cross-section would limit their ability to prevent rotation of the fastener when the shear load is applied. It is readily apparent that additional rigidifying structure is necessary to maintain the stud in relatively fixed position so that it is properly located to withstand the shear load for which it is designed and is not rotated into a position where it is subjected to a tension load and will fail.
The traditional type of fastener element employed today for guard rail fastening is a simple bolt and nut assembly without any additional rigidifying structure to retain the assembly in position for meeting a heavy shear load. Furthermore, the threaded interengagement of bolt and nut is much more time consuming in assembly and disassembly operations, particularly where a damage section is to be replaced, than is desirable in most instances.